The invention relates generally to an apparatus for the production of precast concrete units from prestressed concrete with immediate bonding, and, more particularly, to the production of prestressed concrete beams formed in a continuous manner on a prestressing bed along which extend a plurality of prestressing members or tendons which are tensionable against fixed abutments.
In the prior known technique for producing prestressed concrete ties along a prestressing bed a large number of ties are formed along the entire length of the bed in a plurality of side-by-side rows. This prior technique requires the use of as many concrete forms as there are ties being produced. Typically, the ties are produced in an inverted working position, in which each concrete form shapes the top surface and a rail support arranged on the surface of each of the ties. Fastening elements for the rails are secured in the concrete forms and then concrete is poured into the forms and compressed. When the concrete has set sufficiently, the fastening means for the rail fastening elements are detached from the concrete forms and the fastening elements are removed. After the concrete has completely set, the tendons are detached from the anchoring means of the prestressing bed so that the tension is transmitted to the ties. Subsequently, the tendons between the individual ties are separated, the ties turned over into a working position and the projecting ends of the tendons are then removed.
This previously known method of producing concrete ties requires a great number of concrete forms, since the concrete must harden within the forms. Because the forms are open at the top and the concrete is compressed only as a result of vibrating the forms, the previous technique is not capable of sufficient compression of the concrete which would permit rapid stripping of the forms. Since only rapid stripping of the forms would allow them to be reused, the previously known technique has the disadvantage that a great number of forms are required and cannot be reused.
Accordingly an object of the present invention is to provide an apparatus which permits rapid stripping of freshly poured ties on a prestressing bed during the production of finished members, particularly prestressed concrete ties, so that the number of forms required can be kept at a minimum.
It is another object of the present invention to provide an apparatus capable of the mechanized production of prestressed concrete ties which has superior qualtiy characteristics.
Other objects, features and advantages of the present invention will become more apparent from the description of the invention in connection with the accompanying drawings, to be described more fully hereinafter.